ecu mods--elec. boost controllers

[Ameer Antar]

Even if someone gave me a MAC11, I'd still have to send it out and the 
cheapest I've seen is $400 at 2Bennet. And I don't wanna even deal w/ 
changing over. They are similar ECU's but the wastegate control circuit is 
totally different [I'd prolly need an MC wastegate freq. valve and piping], 
as well as the differences I already stated in regards to compression 
ratios. I'd rather modify an ecu that was designed for my car, than modify 
one that wasn't...For me, I don't think a MAC 11 is an option.

I also started thinking about what some people said, and I really 
appreicate your comments. But actually any mod, other than physically 
limiting boost pressure to the sensor, will max out at 2.0 bar since the 
sensor is seeing full boost. The 2 bar sensor issue could be dealt w/ in 2 
ways. Limit the boost to something like 1.8 bar. Or throw in yer own 50psi 
sensor. Digikey has some for $17, and I'm sure there are other sources, 
such as Allied...Actually it'd give me better control cuz then, all the 
products I'd be working w/ will have their specs known to me. I really 
don't know any specs on the Hitachi sensor. Also last night I was reading 
the LM3914 notes and figured out what the chip does. I could probably get 
the whole kit together using a couple op-amps, a couple relays, voltage 
regulators, plus the new sensor. Although this would be quite a bit more 
expensive than soldering a diode and resistor in there, it would be safer 
b/c it would allow control over the max boost, and the stock gauge will 
work. But the price would be nothing compared to a TAP or IA chipping. 
Since I don't have enough money for the engine my car needs, this might be 
a good time tinker w/ such a ckt. Any other issues you guys can come up with?

-ameer
'84 5kT

At 07:59 AM 10/19/00, you wrote:
>One small problem, Ameer.  The usual pressure transducer in most Audi ECUs 
>has a functional range of from zero bar to 2 bar and then flatlines above 
>2.0 bar.  Those are absolute pressures. Xero bar is total vacuum.  2.0 bar 
>is 2.0 atmospheres of pressure above zero (total vacuum) or 14.7 psi of 
>boost above ambient 1.0 bar.  This is simply not enough range to 
>accommodate 18 to 30 or more psi of boost.  There are 3 bar PTs available 
>but they are a special purchase item which come along with their own 
>software in chip form.
>
>At 03:25 AM 10/19/00, you wrote:
>
>>so what's the actual fuel cutoff point for the MAC 7 or 11? I thought it 
>>was 1.6 bar, but I've heard other #'s...
>>
>>anyway, i thought about this a bit more, and some searching, and what I 
>>thought of is using a bar display driver chip on the ECU pressure sensor. 
>>Basically I'd have to pull the sensor board off and add a few circuits to 
>>it. The bar graph display driver is basically a graphical voltmeter. You 
>>can think of it as an a/d converter. It monitors the pressure sensor 
>>voltage and displays an turns on up to 10 led drivers to display voltage 
>>as a number of lit led's. The chips can actually be chained to get finer 
>>resolution using 30, 40, or more led's. W/ some adjustment I could get 
>>the 2 particular led drivers to turn on at the sensor voltages for 1.4 
>>bar and 1.8 bar. Using a couple solid-state relays on those 2 led drivers 
>>could switch the output to the ecu from 3 different sources. In the 0-1.4 
>>bar range, the output to ecu would be direct from the pressure sensor 
>>[eg. 0-3.5V]. From 1.4-1.8 bar the ecu would get a regulated voltage 
>>which corresponds to 1.4 bar [eg. 3.5V]. Then above 1.8, it would get a 
>>divided voltage from the pressure sensor, making the ecu see 1.54 bar at 
>>1.9 bar actual, 1.62 bar at 2 bar, and so on. The stock boost gauge could 
>>be kept accurate if you just hooked it directly to the pressure sensor 
>>output. This mod allows for normal operation under 1.4 bar, then the ecu 
>>will think the pressure is 1.4 throughout the 1.4-1.8 range. Beyond that, 
>>the ecu will start to see that there is overboost, and eventually cut off 
>>the fuel at the perceived 1.6 bar. Let me know what you guys think.
>>
>>
>>
>>
>>
>>
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>Bob
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